Efficient IP multicast bridging in ethernet switches

ABSTRACT

A switch includes a plurality of ports. A memory stores a bridge table including an entry that associates an Internet Protocol (IP) multicast destination address and an IP source address with a port indicator, which identifies one or more of the plurality of ports. When the switch receives an Ethernet packet comprising an IP multicast packet, a controller generates a key based on an IP multicast destination address and an IP source address associated with the Ethernet packet and performs a lookup on the bridge table using the key. The controller floods the Ethernet packet to the one or more ports identified by the port indicator in response to confirming that the entry is an IP multicast entry and determining that the IP multicast destination address and the IP source address of the entry matches the IP multicast destination address and the IP source address of the Ethernet packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/773,474, filed Feb. 5, 2004, now U.S. Pat. No. 7,590,114 issued Sep.15, 2009, which claims the benefit of U.S. Provisional PatentApplication No. 60/457,397 entitled “A Method For Efficient IP MulticastBridging In Ethernet Switches,” filed Mar. 24, 2003, the disclosuresthereof incorporated by reference herein in their entirety.

BACKGROUND

The present invention relates generally to data communications. Moreparticularly, the present invention relates to multicast bridging innetwork switches.

A packet in a packet-switching network such as an Ethernet network canbe sent in one of three ways: unicast, multicast, and broadcast. Aunicast packet is directed to a single port. A broadcast packet isdirected to all of the ports of the network. A multicast packet isdirected to a group of the ports of the network. Multicast packets canbe either link-layer multicast packets, such as media access control(MAC) multicast packets, or Internet Protocol (IP) multicast packets.

Ethernet switches compliant with the IEEE 802.1D-1998 specification arerequired to switch MAC multicast packets based on the destination MACaddress of the packet. Ethernet switches compliant with the IEEE802.1D-1998, 802.1p and 802.1q specifications are required to switch MACmulticast packets based on the destination MAC address and Virtual LocalArea Network (LAN) Identifier (VLAN ID) of the packet. Such switchescomprise forwarding databases (FDB) that associate each MAC address (orMAC address and VLAN ID combination) with one or more of the ports ofthe switch.

However, most multicast packets are IP multicast packets, which shouldbe flooded according to the source IP address and IP multicastdestination (also referred to as IP multicast group). The InternetEngineering Task Force (IETF) mandates that IP multicast traffic shouldbe encapsulated in a link-layer MAC multicast packet when sent overEthernet. Unfortunately, Ethernet switches handle IP multicast packetsinefficiently, without regard to the source IP address, according to theMAC destination address only. And because a MAC destination address canmap to more than one IP multicast group (32 unique IP multicastaddresses map to each MAC multicast address), an IP multicast packet isoften flooded to more than one IP multicast group, causing unnecessarynetwork traffic, security breaches, and switch workload.

For example, consider a switch having four ports p1, p2, p3, and p4.Assume that two IP multicast groups, IPMG1 and IPMG2, are mapped to asingle MAC multicast destination address MMDA, that IP multicast groupIPMG1 is mapped to ports p1 and p2, and that IP multicast group IPMG2 ismapped to ports p3 and p4. Therefore MAC multicast destination addressMMDA is mapped to all four ports. When an IP multicast packet arrivesfor IP multicast group IPMG1, it is flooded not only to ports p1 and p2,but also to ports p3 and p4. Similarly, IP multicast packets for IPmulticast group IPMG2 are flooded to all four ports.

A similar problem occurs in Ethernet switches that comply with theInternet Group Membership Protocol (IGMPv3). According to the IGMPprotocol, a port can ask to receive all of the traffic sent from an IPsource address to an IP multicast destination address. However, becauseEthernet switches forward IP multicast packets without regard to thesource IP address, the port will receive all of the traffic sent to thatIP multicast destination address from any IP source address, thusunnecessarily burdening the port and the network.

SUMMARY

In general, in one aspect, the invention features a method, apparatus,and computer program. The apparatus comprises a plurality of ports eachadapted to receive Ethernet packets; and a data-link layer switchcontroller, when one of the Ethernet packets comprises an Internetprotocol (IP) multicast packet comprising an IP multicast destinationaddress and an IP source address, to select one or more of the portsbased upon the IP multicast destination address and the IP sourceaddress; wherein the selected one or more ports transmit the Ethernetpacket.

Particular implementations can include one or more of the followingfeatures. The IP multicast packet comprises a virtual local area networkidentifier (VLAN ID); and the data-link layer switch controller, isfurther to select the one or more of the ports based upon the IPmulticast destination address, the IP source address, and the VLAN ID.The apparatus further comprises a memory to store associations betweenIP addresses and the ports; wherein, to select one or more of the portsbased upon the IP multicast destination address and the IP sourceaddress, the data-link layer switch controller is further to select theone or more of the ports based upon the associations stored in thememory. To select one or more of the ports based upon the IP multicastdestination address and the IP source address, the data-link layerswitch controller is further to identify one of the associations storedin the memory based on the IP multicast destination address and the IPsource address; and to confirm the association is an association betweenan IP address and the ports. To identify one of the associations storedin the memory based on the IP multicast destination address and the IPsource address, the data-link layer switch controller is further togenerate a key based on the IP multicast destination address and the IPsource address; and to identify the one of the associations based on thekey. To confirm the association is an association between an IP addressand the ports, the data-link layer switch controller is further todetermine whether the association is marked as an IP multicastassociation. To determine whether the association is marked as an IPmulticast association, the data-link layer switch controller is furtherto determine whether a flag stored in the memory and corresponding tothe association is set. The data-link layer switch controller, when thedata-link layer switch controller cannot identify one of theassociations stored in the memory based on the IP multicast destinationaddress and the IP source address, is further to generate a messagerequesting the creation of an association for the IP multicastdestination address and the IP source address. The data-link layerswitch controller, when the data-link layer switch controller cannotidentify one of the associations stored in the memory based on the IPmulticast destination address and the IP source address, is further totransmit the Ethernet packet from the ports as destination unknown. Theapparatus further comprises a central processing unit to create theassociation for the IP multicast destination address and the IP sourceaddress. The data-link layer switch controller, when one of the Ethernetpackets comprises a Media Access Control (MAC) multicast packetcomprising a MAC multicast destination address and does not comprise anIP multicast packet, is further to select one or more of the ports basedupon the MAC multicast destination address; wherein the selected one ormore ports transmit the Ethernet packet. The MAC multicast packetcomprises a virtual local area network identifier (VLAN ID); and thedata-link layer switch controller, is further to select the one or moreof the ports based upon the MAC multicast destination address and theVLAN ID. The apparatus further comprises a memory to store associationsbetween MAC addresses and the ports; wherein, to select one or more ofthe ports based upon the MAC multicast destination address, thedata-link layer switch controller is further to select the one or moreof the ports based upon the associations stored in the memory. To selectone or more of the ports based upon the MAC multicast destinationaddress, the data-link layer switch controller is further to identifyone of the associations stored in the memory based on the MAC multicastdestination address; and to confirm the association is an associationbetween a MAC address and the ports. To identify one of the associationsstored in the memory based on the MAC multicast destination address, thedata-link layer switch controller is further to generate a key based onthe MAC multicast destination address; and to identify the one of theassociations based on the key. To confirm the association is anassociation between a MAC address and the ports, the data-link layerswitch controller is further to determine whether the association ismarked as a MAC multicast association. To determine whether theassociation is marked as a MAC multicast association, the data-linklayer switch controller is further to determine whether a flag stored inthe memory and corresponding to the association is clear. The apparatusfurther comprises a memory to store a bridge table comprising aplurality of entries each identifying one or more of the ports andaddressable by a key; wherein, to select one or more of the ports basedupon the IP multicast destination address and the IP source address, thedata-link layer switch controller is further to generate the key basedupon the IP multicast destination address and the IP source address;wherein, to select one or more of the ports based upon the MAC multicastdestination address, the data-link layer switch controller is further togenerate the key based upon the MAC multicast destination address; andwherein the selected ports are the ports identified by the bridge tableentry addressed by the key. An integrated circuit comprises theapparatus. An Ethernet switch comprises the apparatus.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an Ethernet switch according to a preferred embodiment ofthe present invention.

FIG. 2 shows a forwarding process for the switch of FIG. 1 according toa preferred embodiment of the present invention.

The leading digit(s) of each reference numeral used in thisspecification indicates the number of the drawing in which the referencenumeral first appears.

DETAILED DESCRIPTION

Embodiments of the present invention comprise a data-link layer (thatis, Open Systems Interconnection (OSI) layer 2) switch controllercapable of flooding Ethernet packets encapsulating Internet Protocol(IP) multicast packets based on the IP multicast destination address andIP source address. In contrast to network layer (that is, OSI layer 3)and multi-layer switch controllers, data-link layer switch controllersdo not execute network layer protocols, as is well-known in the relevantarts. Further, while network layer and multi-layer switch controllersrequire separate dedicated network-layer forwarding databases, alink-layer switch controller requires only a bridge table. Embodimentsof the data-link layer switch controllers according to the presentinvention are able to flood Ethernet packets encapsulating IP multicastpackets based on the IP multicast destination address and IP sourceaddress using the same bridge table that is used for Ethernet bridging.

When an Ethernet packet is received, the switches of the presentinvention determine whether the Ethernet packet comprises an IPmulticast packet. If so, the switch determines whether the bridge tablein the switch contains an entry for the IP multicast destination addressand IP source address. If so, the switch floods the Ethernet packetaccording to that entry. If the IP multicast packet also comprises avirtual local area network identifier (VLAN ID), the switch floods theEthernet packet according to the IP multicast destination address, theIP source address, and the VLAN ID. But if the bridge table does notcontain an entry for the IP multicast destination address and IP sourceaddress, the switch optionally sends a message to the central processingunit (CPU) in the switch to request that an entry in the bridge table becreated.

The Ethernet switch is also capable of flooding Ethernet packetsencapsulating Media Access Control (MAC) multicast packets that do notencapsulate IP multicast packets based on the MAC multicast destinationaddress in the MAC multicast packet. When an Ethernet packet isreceived, the switch determines whether the Ethernet packet comprises aMAC multicast packet that does not encapsulate a IP multicast packet. Ifso, the switch determines whether the bridge table in the switchcontains an entry for the MAC multicast destination address in the MACmulticast packet. If so, the switch floods the Ethernet packet accordingto that entry. If the MAC multicast packet also comprises a virtuallocal area network identifier (VLAN ID), the switch floods the Ethernetpacket according to the MAC multicast destination address and the VLANID.

FIG. 1 shows an Ethernet switch 100 according to a preferred embodimentof the present invention. Ethernet switch 100 comprises a switch 102,which can be fabricated as a single integrated circuit, and a centralprocessing unit (CPU) 104. Switch 102 comprises a controller 112 and aCPU interface 106 to permit controller 112 to communicate with CPU 104.Switch 102 also comprises a plurality of ports 114A through 114N forexchanging Ethernet packets of data with a network 116 under the controlof controller 112 and according to the contents of a bridge table 110stored in a memory 108.

FIG. 2 shows a forwarding process 200 for the controller 112 of theswitch 102 of FIG. 1 according to a preferred embodiment of the presentinvention. Process 200 begins when switch 102 receives an Ethernetpacket (step 202). Controller 112 determines whether the Ethernet packetcomprises an IP multicast packet (step 204) according to conventionaltechniques, preferably by examining the contents of the packet for aknown bit pattern that identifies the packet as an IP multicast packet.

If the Ethernet packet comprises an IP multicast packet, then controller112 generates a key based on the IP multicast destination address, IPsource address, and if present, VLAN ID in the IP multicast packet andperforms a lookup (step 206) on bridge table 110 using the key, whichcan be generated according to conventional techniques, for example byhashing the IP multicast destination address, IP source address, and ifpresent, VLAN ID using a hash function.

Controller 112 then confirms that the entry in bridge table 110indicated by the key is an IP multicast entry (step 208). Each entry inbridge table 110 includes an IP multicast flag that, if set, marks theentry as an IP multicast entry. Each IP multicast entry contains anassociation between an IP multicast destination address, an IP sourceaddress, an optional VLAN ID, and a port indicator that identifies oneor more of the ports 114.

The port indicator can be a vector comprising a bit representing eachport 114, a list of identifiers of one or more ports 114, a pointer tosuch a port vector or port list, or the like.

If in step 208 controller 112 finds the IP multicast flag in the entryis set, then controller 112 determines whether the IP multicastdestination address, the IP source address, and if present, VLAN ID inthe entry match the IP multicast destination address, IP source address,and if present, VLAN ID in the IP multicast packet (step 210). If theymatch, then controller 112 floods the Ethernet packet according to theport indicator in the entry (step 212), and process 200 is done (step214).

However, if in step 208 the IP multicast flag is clear, or if in step210 the IP multicast destination address, the IP source address, and ifpresent, VLAN ID in the entry do not match the IP multicast destinationaddress, IP source address, and if present, VLAN ID in the IP multicastpacket, controller 112 performs another lookup (step 206) on bridgetable 110 based on the lookup algorithm. If the lookup algorithmfinishes with no entry matched (step 209), then controller 112 floodsthe Ethernet packet as destination address unknown (step 216) andoptionally generates a message to CPU 104 requesting the creation of anentry in bridge table 110 for the IP multicast destination address, IPsource address, and if present, VLAN ID (step 218). Of course, othertechniques can be used for notifying CPU 104 and programming bridgetable 110. In response, CPU 104 creates such an entry in bridge table110, and sets the IP multicast flag for the entry. Then process 200 isdone (step 214).

However, if at step 204 the Ethernet packet does not comprise an IPmulticast packet, controller 112 determines whether the Ethernet packetcomprises a Media Access Control (MAC) multicast packet (step 220)according to conventional techniques, preferably by examining thecontents of the packet for a known bit pattern that identifies thepacket as a MAC multicast packet.

If the Ethernet packet comprises a MAC multicast packet, then controller112 generates a key based on the MAC multicast destination address, andif present, VLAN ID in the MAC multicast packet and performs a lookup(step 222) on bridge table 110 using the key, which can be generatedaccording to conventional techniques, for example by hashing the MACmulticast destination address, and if present, VLAN ID using a hashfunction.

Controller 112 then confirms that the entry in bridge table 110indicated by the key is not an IP multicast entry (step 224) by testingthe IP multicast flag. Each MAC multicast entry contains an associationbetween a MAC multicast destination address, an optional VLAN ID, and aport indicator that identifies one or more of the ports 114. The portindicator can be a vector comprising a bit representing each port 114, alist of identifiers of one or more ports 114, a pointer to such a portvector or port list, or the like.

If in step 224 controller 112 finds the IP multicast flag in the entryis clear, then controller 112 determines whether the MAC multicastdestination address, and if present, VLAN ID in the entry match the MACmulticast destination address, and if present, VLAN ID in the MACmulticast packet (step 226). If they match, then controller 112 floodsthe Ethernet packet according to the port indicator in the entry (step228), and process 200 is done (step 214).

However, if in step 224 the IP multicast flag is set, or if in step 226the MAC multicast destination address, and if present, VLAN ID in theentry do not match the MAC multicast destination address, and ifpresent, VLAN ID in the MAC multicast packet, controller 112 performsanother lookup (step 222) on bridge table 110 based on the lookupalgorithm. If the lookup algorithm finishes with no entry matched (step225), then controller 112 floods the Ethernet packet as destinationaddress unknown (step 230) and generates a new MAC multicast entry inbridge table 110 according to conventional methods, ensuring that the IPmulticast flag for the entry is clear (step 232). Then process 200 isdone (step 214).

If at step 220 the Ethernet packet comprises neither an IP multicastpacket nor a MAC multicast packet, controller 112 floods the Ethernetpacket normally, according to conventional techniques (step 234).

The invention can be implemented in digital electronic circuitry, or incomputer hardware, firmware, software, or in combinations of them.Apparatus of the invention can be implemented in a computer programproduct tangibly embodied in a machine-readable storage device forexecution by a programmable processor; and method steps of the inventioncan be performed by a programmable processor executing a program ofinstructions to perform functions of the invention by operating on inputdata and generating output. The invention can be implementedadvantageously in one or more computer programs that are executable on aprogrammable system including at least one programmable processorcoupled to receive data and instructions from, and to transmit data andinstructions to, a data storage system, at least one input device, andat least one output device. Each computer program can be implemented ina high-level procedural or object-oriented programming language, or inassembly or machine language if desired; and in any case, the languagecan be a compiled or interpreted language. Suitable processors include,by way of example, both general and special purpose microprocessors.Generally, a processor will receive instructions and data from aread-only memory and/or a random access memory. Generally, a computerwill include one or more mass storage devices for storing data files;such devices include magnetic disks, such as internal hard disks andremovable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM disks. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits).

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other implementations are within the scope of the followingclaims.

1. A switch comprising: a plurality of ports; a memory configured tostore a bridge table, the bridge table including an entry thatassociates an Internet Protocol (IP) multicast destination address andan IP source address with a port indicator, the port indicatoridentifying one or more of the plurality of ports; and a controllerconfigured to, in response to the switch receiving an Ethernet packetcomprising an IP multicast packet, generate a key based on an IPmulticast destination address and an IP source address associated withthe Ethernet packet; perform a lookup on the bridge table using the key;and flood the Ethernet packet to the one or more ports identified by theport indicator in response to confirming based on the key that the entryin the bridge table is an IP multicast entry, and determining, if theentry is confirmed as an IP multicast entry, that the IP multicastdestination address and the IP source address of the entry matches theIP multicast destination address and the IP source address of theEthernet packet.
 2. The switch of claim 1, wherein the controller isconfigured to generate the key by hashing the IP multicast destinationaddress and the IP source address of the Ethernet packet.
 3. The switchof claim 1, wherein: the entry further associates a virtual local areanetwork identifier (VLAN ID) with the port indicator; and the controlleris further configured to flood the Ethernet packet to the one or moreports identified by the port indicator in response to the VLAN ID of theentry matching a VLAN ID of the Ethernet packet.
 4. An Ethernet switchcomprising: the switch of claim 1; and a central processing unit (CPU)in communication with the switch.
 5. A method comprising: storing abridge table in a memory, the bridge table including an entry thatassociates of an Internet Protocol (IP) multicast destination addressand an IP source address with a port indicator, the port indicatoridentifying one or more of ports of a switch; generating a key based onan IP multicast destination address and an IP source address associatedwith an Ethernet packet; performing a lookup on the bridge table usingthe key; and flooding the Ethernet packet to the one or more portsidentified by the port indicator in response to confirming based on thekey that the entry in the bridge table is an IP multicast entry, anddetermining, if the entry is confirmed as an IP multicast entry, thatthe IP multicast destination address and the IP source address of theentry matches the IP multicast destination address and the IP sourceaddress of the Ethernet packet.
 6. The method of claim 5, whereingenerating the key comprises hashing the IP multicast destinationaddress and the IP source address of the Ethernet packet.
 7. The methodof claim 5, wherein: the entry further associates a virtual local areanetwork identifier (VLAN ID) with the port indicator; and the Ethernetpacket is flooded to the one or more ports identified by the portindicator in response to the VLAN ID of the entry also matching a VLANID of the Ethernet packet.